Date posted: 23rd January 2017

Mould, Windows, Walls, Condensation and Insulation

Rather than being the product of heat loss, black mould and mildew is in most cases caused by inadequate ventilation, particularly in those areas of the home, where air moisture content is high, for example kitchens and bathrooms.

And it’s a problem which effects just as many new homes as it does old ones. Housebuilders are tasked with improving the energy efficiency of new homes. The problem is, not enough focus is put on ventilation - a problem which becomes more acute at this time of year when it’s cold.

In sealing-up our homes more and more effectively, we’re making them warmer and more energy efficient but we’re also giving moisture nowhere to go.

This isn’t a problem in spring, summer and even autumn - most of us open up windows fairly regularly, allowing moisture to escape.

But at this time of year we’re generally far less inclined to open up windows and let some often ‘very fresh air’ in. That means that the moisture from cooking, washing, drying clothes, plus other household activities remains inside the property, causing condensation.

This is a subject that we have touched on previously in our condensation blog. Condensation isn’t the cause of black mould but it is a symptom of inadequate ventilation.

Why does condensation form?

There is a limit to how much water vapour the air can hold. The rule is that the warmer the air, the more vapour it can accommodate, which is why on colder days, condensation is more likely to form.

This will happen if moisture in the air makes contact with a cooler surface, for example outside wall or window. When this happens, the vapour in the air will become more concentrated, forming droplets – condensation.

So if you’re cooking a pot of pasta, without the lid on or don’t open the window or switch on an extractor fan after showering, it’s likely that you’re going so see a build-up of moisture and that can lead to the growth of black mould or mildew. Purchasing a dehumidifier can help keep condensation to a minimum, if you have a real problem that is proving hard to control.

What is black mould?

Black mould and mildew are both common fungi but there are distinctions between them. The first point is that while mildew may not look nice – it usually starts out white and then turns a yellowish colour - it doesn’t really do too much harm. You can identify it as much through that musty smell that it leaves in a room.

Black mould is altogether more sinister and depending on the strain, it can cause asthma, respiratory problems, eye irritation, infections and in its most toxic form – Stachybotrys or ‘toxic black mould’ – can cause headaches, joint pain, dizziness, while it’s also been suggested that it may cause cancer.

What black mould needs is moisture so inadequately ventilated homes, where moisture can collect into droplets, for example bathroom tiles, pipes, or even around windows can be a very real problem.

Why adequate ventilation is key

If you open your windows regularly to vent your home, you lower its moisture levels and make it less likely that condensation will form inside it.

You don’t always, however, want to leave windows open. In cold weather, there’s very little point spending money on insulating your property, only to let warm air escape. This is where trickle vents can come in.

I’m personally no big fan of the way that some trickle vents look but nonetheless, they do have their place and can be important in reducing the build-up of condensation and making it far less likely that black mould and mildew will form in your home.

What are trickle vents?

Trickle vents provide continuous background ventilation, ensuring circulation of air and avoiding build-up of condensation, without allowing the heat in your home to escape.

There are three types of trickle vent – through frame, over frame and glazed-in. Glazed-in ventilation sits at the very top of energy efficient double and triple-glazed windows, while over-frame routes ventilation over the top of the frame into the property.

The most common form of window ventilation is through-frame. This routes fresh-air through the top of the window frame and can be adjusted through a simple open and closing mechanism to provide as much ventilation as required.

Technically there is no specific requirement to install replacement windows with a trickle vent unless there was one there previously. Where this is the case Building Regulations stipulate that as a minimum, the new trickle vent must provide the same amount of ventilation as the one it’s replacing or 5000mm2 EA per habitable room. Good window installers should be able to talk you through the options.

You can stop the build-up of condensation by:

Ventilating rooms regularly and leaving doors open to allow air to circulate, unless you are cooking or showering

When you are cooking, showering or bathing – Ventilate by opening the window, putting the fan on and closing the door of the room you are in.

How to clean mould from windows, walls and tiles

A word of caution: mould can cause allergic reactions and poor health, so if you have an extensive problem with mould on walls, it may be best to seek expert advice. If tackling a smaller area, make sure you wear protective eyewear, gloves, and a face-mask, as contact with the spores can be harmful to your health. Do remember to open windows/doors or use an extractor fan while working in the room.

Make a solution of chlorine bleach and water – usually 1 part bleach to 3 parts water. There is no need to buy expensive cleaning products.

Using a stiff-bristled brush (like an old toothbrush or nailbrush) and scrub the blackened area.

Rinse thoroughly and dry.

Note:- Both distilled white vinegar and hydrogen peroxide will do an effective job of killing mold spores in porous materials. Bleach can only kill mold on non-porous surfaces, as it does not penetrate porous surfaces; so mould roots are left to grow again.

Closing thoughts

Black mould is pretty indiscriminate. You can see it in new homes and older properties but what is consistent across the board is that ventilation and condensation is always an issue. New windows and doors will make it less likely that you’ll be peering out through misty windows and keep your home warmer but energy efficient double and triple-glazed windows aren’t a solution in themselves.

Moisture in the air condenses on the coldest surfaces it comes into contact with. If it’s not your windows, it’s going to condense somewhere else and where it does condense mould can form.

Opening windows regularly to vent the air inside is the most effective solution. If it’s too cold or you don’t want to, trickle vents, which can also be fitted retrospectively, can significantly improve ventilation inside your home, helping to remove the moisture, which is key to the growth of black mould.

For more information on our range of energy efficient windows and doors call or email me or the sales team on 01264 359355 or sales@kjmgroup.co.uk.